= Operands

.Syntax
[source,unlang]
----
string
integer
"double-quoted string"
'single-quoted string'
`back-quoted string`
----

Any text not matching xref:unlang/attr.adoc[&Attribute-Name] or a
xref:unlang/condition/return_codes.adoc[return code] is interpreted as a value for a
particular xref:type/index.adoc[data type].

Double-quoted strings and back-quoted strings are dynamically expanded
before the condition is evaluated.  Single-quoted strings are static
literals and are not dynamically expanded.

When used as an existence check, the condition evaluates to `true` if
the data is non-zero.  Otherwise, the condition evaluates to `false`.

For integer existence checks, `0` is `false`; all other values are `true`.

For string existence checks, an empty string is `false`.  All other
strings are `true`.

All other data types are disallowed in existence checks.

.Examples

`"hello there"` +
`5`

// Copyright (C) 2021 Network RADIUS SAS.  Licenced under CC-by-NC 4.0.
// This documentation was developed by Network RADIUS SAS.
